1. Field of the Invention
The present invention relates to a liquid-crystalline polymer which has the high strength (with small anisotropic variation) and exhibits the anisotropism in its molten state.
2. Discussion of Related Art
Liquid-crystalline polymers which exhibit the anisotropism in their molten state have recently been attracting attention because of their high strength, high heat resistance, and superior moldabiltiy. A variety of liquid-crystalline polymers have been proposed so far; and typical ones are disclosed in Japanese Patent laid-open Nos. 72393/1974, 43223/1975, and 50594/1979. All of these polymers have a skeleton composed of rigid monomers so that they exhibit liquid-crystalline properties and provide high strength and good processability.
Liquid-crystalline polymers, however, have a disadvantage in that they are extremely susceptible to orientation because they have rigid skeletons. The susceptibility to orientation leads to the anisotropy of orientation and strength, with the result being in that the molded articles formed from these liquid-crystalline polymers are subject to fibrillation. The attempts made so far to reduce the anisotropism, include the introduction of soft spacers into the rigid skeleton and the introduction of reinforcements into the polymer. The former sacrifices the high strength ascribing to the rigidity, and the latter, the sacrifices the characteristic properties of the resin such as light weight, chemical resistance, and modability. Reducing the anisotropism of strength without impairing the superior mechanical strength of the rigid polymer is very important in increasing the dimensional accuracy of precision parts and to produce film having high mechanical strength.
The present inventors carried out extensive studies noticing that the polymer having the naphthalene skeleton in the main chain (as typified by Japanese Patent Laid-open No. 50594/1979) has high strength and superior melt-processability although it is composed of p-position benzene rings and naphthalene rings and is not incorporated with the so-called soft spacer. The results of the studies led to the present invention.